Sanding machine

ABSTRACT

This disclosure relates to a sanding machine for use in sanding and refinishing horizontal surfaces. The sanding machine includes a frame movably mounted on drive wheels which permit the machine to move longitudinally along the horizontal surface. Forward and rear rollers are rotatably mounted on the frame and carry an endless abrasive belt. The forward roller is contiguous to the horizontal surface while the rear roller is positioned above and to the rear of the forward roller so that the belt is angularly disposed with respect to the horizontal surface. The belt is held in contact with the horizontal surface by a platen located behind the forward roller and secured to the frame. The rear roller is driven and imparts movement to the endless belt. Horizontal leveling means permit the platen to be maintained in a level position transverse to the direction of movement of the machine. A belt tracking means maintains the endless belt in a preselected tracking position with respect to the forward and rear rollers.

United States Patent 11 1 Sharpless 1111 3,744,188 14 1 July 10, 1973 SANDING MACHINE [76] Inventor: Samuel H. Sharpless, 6l-67 N. Pine St., l-lazleton, Pa. 18201 22 Filed: Mar. 29, 1971 21 Appl.No.: 128,679

Primary Examiner-James L. Jones, Jr. Attorney-Jones & Lockwood [57] ABSTRACT This disclosure relates to a sanding machine for use in sanding and refinishing horizontal surfaces. The sanding machine includes a frame movably mounted on drive wheels which permit the machine to move longitudinally along the horizontal surface. Forward and rear rollers are rotatably mounted on the frame and carry an endless abrasive belt. The forward roller is contiguous to the horizontal surface while the rear roller is positioned above and to the rear of the forward roller so that the belt is angularly disposed with respect to the horizontal surface. Tli belt is held in contact with the horizontal surface by a platen located behind the forward roller and secured to the frame. The rear roller is driven and imparts movement to the endless belt. Horizontal leveling means permit the platen to be maintained in a level position transverse to the direction of movement of the machine. A belt tracking means maintains the endless belt in a preselected tracking position with respect to the forward and rear rollers.

26 Claims, 12 Drawing Figures Pmmguwu 3.744.188

INVENTOR SAMUEL H. SHARPLESS W MM A TTORNEYS PAIENIEU JUL 1 0 ms.

SHEETS? w wmw wk mmw SHE! 5 0f 7 m m \k wk R MN \\v/\\\ I! i4 0 0 r 4 I .wv r F vow mm? 3 3 KY 0 FL. W 0 bmw vm 9 1 1 wk k5 wk 5 w KS Q um mm mww wmw E m q PAIENIEU JUL 1 0 I973 SANDING MACHINE BACKGROUND OF THE INVENTION This invention relates to a sanding machine for use in sanding and refinishing horizontal surfaces, and more particularly to a machine for maintaining and refinishing bowling alley lanes.

Many types of sanding machines are known for refinishing horizontal surfaces; for example, rotary type sanders have been used to refinsh floors, and endless belt type sanders have been used to refinish bowling lanes. One of the major problems that has developed with respect to sanding machines of both the circular and the endless belt types is the difficulty of maintaining the machines at a level position during the sanding operation. This is a particularly acute problem in the maintenance of bowling alleys, for there the continuous use of a bowling lane produces grooves and ruts. Such grooves develop in the lane because most bowlers roll the ball along approximately the same path, and the force of the bowling ball repeatedly striking the lane damages the wooden surface and its finish. It is necessary, therefore, to refinish the bowling lanes periodically to elimiate these grooves and ruts and to maintain the horizontal surface that is required to enable the bowling balls to roll true. To assure that this finishing operation will produce the desired results, it is of utmost importance to maintain any sanding and refinihsing machine in a horizontal position during its operation.

Many attempts have been made to provide leveling devices for bowling lane sanders; however, most of the previous devices have been found to be inaccurate, and it has been found that it is difficult to meet the standards which are required to insure that the lanes are maintained in a horizontal plane. Although previously known sanding machines may eventually produce a horizontal surface which will meet the requirements of a bowling lane it is a very tedious and time-consuming process, since the controls are generally complex and do not respond with sufficient speed, and it is necessary to make several passes over the lane to accomplish the job.

Another problem which has plagued the endless belt sanders which are presently used in bowling lane refinishing is maintaining the belt in the preselected tracking position. Previously, guides or other cumbersome controls have been used, but is has been found that corrective action must taken almost instantaneously, or else the belt will move too far off the drive rollers and require that the machine be shut down before the position of the belt can be corrected, and prior art machines cannot provide such a fast response. This increases the time and labor costs for doing the job and thus increases the total cost of the job.

Although bowling lane sanding would be the principle type of sanding job in which the subject invention might be used, there are many other industrial applications, such as floor sanders and the like, wherein a leveling mechanism and an automatic belt tracking or belt positioning mechanism could be used in order to reduce the time required for the job as well as the cost of many sanding and refinishing jobs.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide a sanding machine for use in sanding and refinishing horizontal surfaces and effectively and precisely maintaining the surface horizontal.

Another object of this invention is to provide an sanding machine which can be used to resurface bowling lanes.

Another object of this invention is to provide a mechanism for maintaining a level sanding surface so that the surface which is being refinished will be maintained in a horizontal plane.

Another object of this invention is to provie a sanding machine with an abrasive, endless belt provided with a mechanism to maintain proper tracking of the belt.

Another object of this invention is to provide a sanding machine which is simple and easily transportable to the place of operation without the necessity of dismantiling and reassembling the machine.

Still another object of this invention is to provide a sanding machine which is motor driven during the sanding operation.

Another object of this invention is to provide a mechanism to adjust the path of travel of one side of an end less belt whereby the belt can be maintained in a preselected position.

Another object of this invention is to provide a bowling lane sanding machine with an improved leveling mechanism to insure that the lane is level in the transverse direction and that the lane conforms to the original condition in its longitudinal direction.

Still another object of this invention is to provide a sanding machine having pickup wheels which permit the machine to be lfited off the horizontal surface which is to be sanded, thereby p ermitting initial positioning of the sanding machine and repairs.

These and other objects are accomplished by the present invention through the use of a sanding machine including a support frame which is mountd for movement in a longitudinal direction on drive wheels which contact a horizontal surface to be sanded. The drive wheels are carried on axles which are driven by a re versible variable speed motor permitting the frame to be maneuvered in a forward and rearward direction at varying speeds. The drive wheel axles are journaled in a pair of axle support bearing assemblies, one of the bearing assembles being pivotally mounted to the frame while the other bearing assembly is pivotally mounted to a yoke. One end of the yoke is pivotally mounted to the frame while the other end of the yoke is in contact with a cam. The cam is carried on a rotatable shaft which in turn is driven by a leveling motor controlled by a remote switch. Movement of the leveling cam causes the yoke to be moved upwardly and downwardly with respect to the frame, causing one of the bearing assemblies which carry the drive wheel axles to be moved upwardly and downwardly, thus raising and lowering one side of the frame. This mechanism provides a transverse leveling for the machine.

The frame carries forward and rear parallel, spaced rollers which are circumscribed by an endless abrasive belt. The forward roller is pivotally connected to the forward end of the frame and is contiguous to the floor. A platen located behind the forward roller and secured to the frame holds the abrasive belt in contact with the horizontal surface being sanded. The rear roller, which is serrated, is connected to a drive motor through a pulley arrangement, whereby motion is imparted to the endless belt.

A belt tracking mechanism maintains the abrasive belt on the rollers in a preselected position. The tracking mechanism includes an spring biased lever switch which is secured to the frame and is in contact with one edge of the abrasive belt so that if the belt begins to track improperly the lever switch operates a series of microswitches which in turn activate a reversible drive motor which is carried on the frame. The tracking drive motor is connected to a shaft through a pulley arrangement. The shaft is suitably joumalled in the frame and extends towards the forward roller of the sanding machine. At the forward end of the shaft is a tacking cam which is engaged by a needle bearing on the rearward end of a tracking lever.

The forward roller is carried by a pair of pivot arms which are mounted on support shafts extending outwardly from each side of the forward end of the frame. The pivot arms have spring loaded pistons, thus putting tension on the belt when the forward roller is pivoted to a horizontal slightly above and parallel to the horizontal surface. One ofthe pivot arms is secured from movement when the forward roller is pivoted to the horizontal position while the other pivot arm is free to pivot about its support shaft.

A sleeve integral with the movable pivot arm and encompassing its support shaft has an aperture through which the tracking lever extends so that the tracking lever also pivots about the pivot arm support shaft. Perpendicular to and formed integrally with the sleeve is an arm which carries a lug through which the tracking lever extends. Extending inwardly from the lug is a holding member which encircles the pivot arm. Therefore, when the tracking lever is pivoted about the pivot arm support shaft, the pivot arm is pivoted also. A tab formed integrally with the holding member and extending inwardly is engaged by a spring positioned between the platen and the tab. The spring is in compression and imparts an upward force on the tab so that the movable pivot arm is biased upwardly.

The tracking cam, which is in contact with the needle bearing on the rear end of the tracking lever, will move the rear end of the tracking lever upwardly or downwardly depending on its position. If the tracking cam is moved to the high position, the rear end of the tracking lever is moved upwardly and the forward end moves downwardly since the lever is pivoted about the pivot arm support shaft. The downwardly movement of the forward end of the lever imparts a downward movement to the holding member, thus the pivot arm will be pivoted downwardly also. When the tracking cam is moved to the low position, the compression spring between the tab on the holding member and the platen forces the pivot arm upwardly and the contact between the needle bearing and the cam is maintained.

The rotation of the tracking cam will cause the movable pivot arm to change position, thereby adjusting the path of travel of one side of the endless belt. The way the path is adjusted is dependent on which direction the endless belt moves from its preselected position on the rollers which is determined by the switch lever contacting the belt.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and additional objects, features and advantages of the present invention will be apparent to those skilled in the art from the following detailed description of a preferred embodiment taken with the accompanying drawings, in which:

FIG. 1 is a perspective view of a sanding machine according to the present invention:

FIG. 2 is a side elevation of the sanding machine according to the present invention with a portion of the guide roller mechanism removed to expose the belt tracking mechanism;

FIG. 3 is a bottom view of the sanding machine according to the subject invention showing the driving and leveling mechanisms;

FIG. 4 is a partial sectional view taken on line 4-4 of FIG. 3;

FIG. 5 is a diagrammatic view of the tracking lever switch according to the subject invention;

FIG. 6 is a prespective of a portion of the belt tracking mechanism according to the present invention:

FIG. 7 is a sectional view taken on line 7-7 of FIG.

FIG. 8 is a rear elevation of the sanding machine according to the subject invention;

FIG. 9 is an elevation of the sanding machine opposite that shown in FIG. 2; I

FIg. 10 is an elevation view similar to the view shown in FIG. 9, with the forward roller positioned in the up position for installation of the endless abrasive belt;

FIG. 11 is a diagrammatic view of the sanding machine according to the subject invention in the trans porting position; and

FIG. 12 is a schematic of the drive, belt drive, leveling and tracking control circuit of the sanding machine according to the subject invention.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring more particularly to the drawings in FIGS. 1 and 2, the numeral 10 indicates a sanding machine including a frame 12 which is divided into three sections, namely, rear, undercarriage and roller carrying sections, indicated by numberals l4, l6 and 18, respectively. The rear section 14 is composed of members which form generally a rectangular box while the undercarriage section 16 is generally in the form of a right angle triangular prism which provides an incline portion to support the roller carrying section 18, as can be seen in FIG. 2. The roller carrying section 18 includes two parallel side members 20 and 22 which are disposed parallel to the direction of movement of the sanding machine when in operation. A pair of spaced tubular members 24 and 26 extend between the two side members 20 and 22 and are securedto the side memers by welding or other suitable means. The ends of tubular members 24 and 26 extend through the side member 20 and have depending therefrom inclined plates 28 and 30. The frame members can be made of any suitable material which is left to the direction of the user. The side members 20 and 22 carry a forward roller 32 which is pivotally mounted to their forward end and rear drive roller 34 which is suitably joumaled in the side members. A shaft 35 extends through the side member 20 and carries a pulley 36. A V-belt 37 or other suitable means circumscribes pulley 36 and a pulley 38 which is carried on the shaft of a belt drive motor 39 mounted on the frame in any suitable manner. Any other type of arrangement known in the art, such as a chain and sprocket, can be used to drive the rear roller 34, the operation and control of the drive motor will be explained hereinafter. The drive roller 34 is serrated to provide a frictional surface to impart movement to an endless abrasive belt 40 which circumscribes forward roller 32 and rear roller 34 and a platen 41 which is disposed transverse to the direction of movement of the machine and is secured to the forward ends of side members and 22. The method of securing the platen 41 to the side members will be explained hereinafter. As mentioned above, the forward roller 32 is pivotally connected to the frame, this pivotal arrangement permitting easy replacement of the endless belt and providing an automatic belt tracking means which will also be described hereinafter.

Although the sanding machine can be used in any sanding operation where maintaining the surface to be sanded in a horizontal plane is important, one of the primary functions of the sanding machine of the present invention is to refinish bowling lanes, and for the purposes of illustration the sanding device is shown in FIG. 1 in a bowling lane 42. Rear guide wheels 44 and 46 (see FIG. 3) are suitably mounted on adjustable shafts which are secured to rear frame section 14 and extend out from the side of the frame. The guide wheels contact the rails 47 between the bowling lanes. Any suitable means may be used to adjust the position of the rear guide wheels 44 and 46 so that they will conform to any size lane. Forward guide wheels 48 and 50 are connected to the side members 20 and 22, respectively, by pivotal shafts 52 and 54 (FIG. 3) which are also used for the forward roller 32. Forward guide wheel 48 is carried on a shaft 56 which extends through a bracket 58 that is carried on shaft 52. The shaft 56 (FIG. 1) is secured in bracket 58 by a wind bolt which permits the shaft to be positioned longitudinally. The rear end of shaft 56 contacts a ribbon strap 60 which is fixedly secured to the extension of tubular member 24. The for ward guide wheel 48 is offset from the frame to provide room for a portion of the automatic belt tracking mechanim 62. Forward guide wheel 50 is secured to the roller pivot shaft 54 and extends perpendicular to the frame. A dust collection hood nozzle 64 covers the rear portion of the rear drive roller for collecting the dust and other particles when the sanding machine is in operation. The hood nozzle 64 is secured to the side frame members 20 and 22 with screws or other type fasteners. And is connected to a vacuum cleaner through a suitable flexible hose. The vacuum cleaner can be of any standard type known in the art and can be towed by the sanding device if desired.

In order to move the sanding machine into its proper position for operation, there are a pair of rear castors 74 and 76 (see FIG. 3) secured to the bottom member of rear frame section 14. A pair of forward positining or repairing wheels 78 and 80 are rigidly secured to a rotatable shaft 82 by set screws, key and slot, or other suitable means. (See FIG. 4). Shaft 82 is joumaled in lugs 84 and 86 which are fixedly secured to the forward transverse member 88 of the undercarriage frame section 16, The shaft 82 extends through the lug 86 outwardly to an L-shaped bracket 90, which is rigidly secued by any suitable means to the forward inclined plate 28, and is joumalled in the bracket. A bevel gear 92, which is located on the inside of the bracket 90 and is so disposed that the gear teeth face inwardly, is secured to the shaft 82 by a set screw, key and slot, or other suitable means. The gear 92 contacts another bevel gear 94 which is perpendicular thereto and which is rigidly secured to the forward end of a rotatable shaft 96 which extends rearwardly and is supported by an L- shaped bracket 98 and a rear support plate 100 which is secured to the lower portion of the rear frame section 14. The shaft 96 passes through an aperture in inclined plate 30. Near the rear of shaft 96 is an L-shaped lever arrangement 102 which is rigidly secured to the shaft, thus providing a means to rotate the shaft.

When it is desirable to move the sanding machine to an operating position, repair the machine, or replace an abrasive belt, the free leg of the L-shaped operating lever 102 may be lifted upwardly, thus imparting a rotational movement ot shaft 96. The shaft 96 rotates bevel gear 94 which, in turn, rotates bevel gear 92, thereby causing shaft 82 to be rotates. when shaft 82 is rotated forward, positioning wheel assemblies 78 and 80 are pivoted downwardly to engage the horizontal surface or floor so that the forward end of the sanding machine is raised. As the forward end of the sanding machine is raised to a selected height, rear castor wheels 74 and 76 will engage the horizontal surface, thus allowing the sanding machine to be moved and repaired more easily.

BELT TRACK MECHANISM Turning now to the automatic belt tracking mechanism, as explained above forward contact roller 32 is pivotally secured to the forward edge of the frame side members 20 and 22 by a pair of pivot roller arms 104 and 106. Pivotal roller arms 104 and 106 are carried on roller pivot shafts 52 and 54, respectively, which are rigidly seemed to side frames 20 and 22, respectively. The pivot arms 104 and 106 include spring-loaded pistons which force the forward roller 32 outwardly, thus transmitting tension to the belt 40. Since the belt will be in tension, there will be a tendency for the belt to pivot the forward roller 32 upwardly.

The purpose of the automatic belt tracking mechanism is to adjust the path traveled by one side or edge of the abrasive endless belt 40. It is well known in the belt tracking art that if the length of the path of one side of an endless belt which is carried on two parallel rollers is increased or decreased with respect to the length of the path traveled by the other side of the belt, the belt will move on the belt carrying rollers in the direction of the shorter path. Thus, if the path traveled by one side of the endless belt 40 is increased or decreased, the belt will move on rollers 32 and 34 in the direction of the lesser of the two paths. In the present invention, to maintain the belt tracking in its preselected position, a lever switch 108 (see FIGS. 1, 2, and 5) is pivotally secured in any suitable manner to the roller carrier frame section 18. The lever extends above the upper plane of the abrasive belt 40 and is biased inwardly by a spring 1 10 which is secured to the lever and to the frame 18 in any suitable manner. The lever switch 108 has stepped projections 112 and 114 extending outwardly from opposite sides which will contact suitable microswitches 116, 118, and on the right side and microswitches 122, 124, and Y126 that are suitable mounted on the left side of the lever as viewed in FIG. 5. Therefore, if the belt 40 begins to move to the left as viewed in FIG. 5, the belt will force lever 108 to the left thus causing the first stepped projection 114 to contact microswitch 122. On the other hand, if the belt 40 moves to the right, the spring 110 which biases the lever 108 to the right will cause the lever 108 to follow the belt 40, and the first step of the stepped projection 122 will contact microswitch 1 16. The circuitry of the tracking mechanism will be described hereinafter. While operating the sanding machine, if the belt 40 begins to track improperly, the lever switch 108 will contact either microswitch 116 or 122. In order to explain the mechanical phase of the belt tracking mechanism, assume that switch 122 is operated by lever 108. When switch 122 is closed, a reversible tracking motor 126 (see FIGS. 2 and 3) which is carried by a support bracket 128 secured to the rear frame section 14 is energized. The motor shaft carries a pulley 130 which is circumscribed by a Vshaped, toothed belt 132 that also encompasses a pulley 134 secured to the rear end of an inclined shaft 136. The shaft 136 extends through apertures in the inclined plates 30 and 28 and is held in place by a pair of collars 137 and 137' disposed on opposite sides of plate 30. Any other suitable means such as a chain and sprocket can be used to transfer rotational movement of motor 126 to shaft 136.

Secured to the forward end of the shaft 136 is a cam 138 such as an eccentric (see FIG. 6) which is angularly disposed with respect to the horizontal surface 42. The cam 138 is contacted by a needle bearing member or cam follower 140 secured'to the rear end of a tracking lever 142 which extends forward and is parallel to the pivot arm 104. The lever 142 extends through an aperture 146 in sleeve 144 which encircles shaft 52. A threaded fastener 148 such as a machine screw or a wing headed bolt is threaded through a threaded aperture in the sleeve 144 and secures the lever in position. lntegrally formed with the bottom of the sleeve 144 and extending perpendicularly thereto beneath the lever 142 is an arm 150 which has an upwardly extending lug portion 152 extending upwardly through which the lever 142 extends. lntegrally formed with the lug 152 and extending upwardly therefrom is a holding member 154 which encircles pivot arm 104. An inwardly extending tab 156 formed integrally with the holding member 154 is contacted by a bias spring 155 inserted in a recess in the upper surface of platen 41. The spring maintaining an upward force on the holding member 154 which in turn maintains an upward force on the pivot arm 104.

As can be seen in FIG. 6, if the cam 138 is rotated so that the high point is in contact with cam follower 140, the rear end of the lever 142 will move upwardly, thus pivoting the forward end of lever 142 downwardly, the lever pivoting about shaft 52.,If the forward end of lever 142 is moved downwardly, holding member 154 will force the forward end of the pivot arm 104 downwardly to adjust the length of the path traveled by the edge 107 of the belt 40 adjacent arm 104. The pivot arm 106 on the opposite sides of the sander is stationary, being rigidly secured in position, as can be seen in FIG. 3, by a bolt 157 or other suitable means. A downward movement of pivot arm 104 will tend to tilt the forward roller 32 slightly down from the horizontal position thus lengthening the path and causing the abrsasive belt 40 to travel toward pivot arm 104. On the other hand, an upward movement of pivot arm 104 tilts the forward roller 32 slightly upward from the horizontal position, thus causing the belt 40 to travel away from pivot arm 104.

Since it was assumed that the belt 40 was moved to the left, as viewed in FIG. 5, so that switch 122 was operated, it is necessary under these conditions that the path of the edge 107 of belt 40 be increased so that the belt will move to the right. However, if the endless belt 40 begins to move to the right, as viewed in FIG. 5, thus causing the lever arm 108 to move to the right so that projection 112 contacts microswitch 116, the tracking motor 126 is energized in the reverse direction, thus causing the cam 138 to be rotated toward a low point. The spring will force holding member 154 upwardly, thus causing pivot arm 104 to rise slightly, whereby the forward roller 32 will tilt up from the horizontal position and away from its parallel relation with the fixed position of roller 34. It can be seen that if pivot arm 104 is pivoted upwardly, the rear-end of lever 142 will move downwardly due to upward forces applied by spring 155 on holding member 154, thus causing needle bearing 140 to remain in contact with cam 138.

LEVELING MECHANISM Turning now to the leveling mechanism which maintains the level of the frame 12 so that the platen 41 will remain horizontal with respect to the surface 42 being sanded, FIGS. 3, 7 and 8 illustrate a drive motor 158 secured to the undercarriage frame 16 in any suitable manner, and a motor drive shaft 160. The drive motor 158 can be of any standard type; preferably, it will be a reversible, variable speed motor. Connected to drive shaft 160 by a drive sprocket (not shown) is an idler sprocket 164 which is carried on a shaft 168 suitably journaled in lugs 170 and 172 extending rearwardly from the bottom rear cross member 173 of undercarriage frame 16.

Forward and rear drive axles 174 and 176, respectively, each carrying two sets of drive wheels 177, 177 and 178, 178', are carried by axle bearing support assemblies 180 and 182. Axles 174 and 176 carry drive sprockets 183 and 184, respectively, which are circumscribed by a drive chain 185 which also engages the drive sprocket on shaft 160 of motor 158.

Axle support member 180 is pivotally mounted and carried on shaft 168 between sprocket 164 and lug 172. Axle support member 182 is carried by a pivot shaft 186 which is secured between the legs of a leveling yoke assembly 187. The forward end of the legs of yoke assembly 187 are pivotally mounted on shaft 82, which carries the forward positioning wheel. The legs 188 and 190 of yoke assembly 187 extend rearwardly from shaft 82 and are disposed above drive axles 174 and 176, as can be seen in FIG. 7. Pivotal shaft 186 which carrries axle support member 182 is suitably joumated in lugs which depend from legs 188 and 190. Secured between the rear end of legs 188 and 190 is a shaft 192 which carries a cam follower, or bearing collar 194. The bearing collar is contacted by an eccentric cam 196 carried on a rotatable cam shaft 198 (FIG. 8) which is disposed above shaft 192 and extends through and is suitably journaled in upright support members 200 and 202. Cam shaft 198 carries a sprocket 204 an a limit switch box 206. An endless link chain 208 encircles the sprocket 204 and a sprocket 210 carried on the drive shaft 212 of a leveling motor 214. The leveling motor 214 which is secured to the undercarriage frame 16 by an L-shaped bracket 216 or other suitable means, is a reversible motor and is operated by a remote pushbutton switch 218 (not shown).

In order to operate the leveling mechanism, a suitable level sensing device or level bubble of a type known in the art can be used by the operator to determine when the sanding machine is not in a level position. The remote switch 218 can then be depressed to operate the leveling motor in a proper direction, thus causing leveling motor 214 to rotate sprocket 204 through drive sprocket 210 and chain 208. Rotation of sprocket 204 imparts rotation to cam 196 which when rotated will either raise or lower the rear end of yoke 187. If the rear end of yoke 187 is moved downwardly with respect to the frame, the pivot shaft 186 which carries axle support member 182 is also moved downwardly, thus raising the yoke side of the sanding machine. Since axle support member 180 is pivotally mounted on lugs 172 and 170 which are rigidly secured to the bottom transverse member of undercarriage 16, the pivot shaft 168 will not move. Thus, only one side of the sanding device will be raised and lowered to permit the platen to be leveled in a transverse direction. If it is desired to lower the yoke side ofthe sanding machine, the cam 196 is rotated so that the bearing collar 194 contacts a low part of the eccentric on cam 196, thus permitting the rear end of yoke 187 to move upwardly due to the weight of the machine itself. As the rear end of yoke 187 is moved upwardly, the pivot shaft 184 which carries axle support member 182 is also moved upwardly so that the drive wheels 177 and 178 are moved upwardly with respect to the machine frame. As described above, axle support member 180 will remain stationary with respect to the frame. In this manner, the yoke side of the frame may be lowered to permit the platen to be maintained in a level position. The limit switch box is provided to limit the movement of shaft 198, thus limiting the movement of cam 196.

In order to permit the platen 41 to float over the horizontal surface, each end of the platen is secured to the frame side members and 22 by fasteners 220 (FIGI 7) and 220 (not shown) which are secured to universal joints 222 and 222' (not shown) secured to the top surface of platen 41, as can be seen in FIG. 7. The fasteners 220 and 220' can be adjustably secured to the side members 20 and 22in any suitable manner. The platen 41 maintains the abrasive belt 40 in contact with the horizontal surface which is being refinished. Since an abrasive belt will become worn with contin ued use, it is of great importance that a sanding machine be designed to permit an operator to replace a worn belt easily and with the least amount of down time. As can be seen inFIG. 9, one side of the sanding machine according to the present invention has a cover 224 which is hingedly connected to subcarriage frame 16 along hinge means 226 such as a piano hinge. Locating pins 228 and 230 are provided on side member 22 and cooperate with apertures (not shown) in cover 224 to maintain the position of side member 22 above the frame 16. In this preferred embodiment, a latch lever 232 is secured to cover 224 and contacts a latch receiver 234 secured on the top of side member 22; however, any other suitable latching means may be provided.

In order to replace abrasive belt 40, the sanding machine is raised on the forward repair and positioning wheels 78 and 80, as explained above and shown in FIG. 10, so that the platen 41 is no longer in contact with the horizontal surface 42. The securing means holding pivot arms 104 and 106 is released, and the fastener 148 on the belt tracking mechanism (see FIG. 6) is loosened, thus permitting lever 142 to slide forward whereby needle bearing is no longer in contact with cam 138. Upon completion of the abovedescribed manipulations, the roller arms 104 and 106 may be pivoted upwardly, as shown in FIG. 10, which will permit removal of belt 40. Cover 224 is unlatched and is pivoted downwardly along the piano hinge 226 so that the belt 40 can be removed from the rollers. The upper end of the side member 22 preferably is spaced from the undercarriage frame 16 so that the belt will easily slide from underneath the rear roller 34. Upon removal of the worn belt, a new belt may be slipped onto the roller frame, and the sanding machine may be returned to its operating mode by reversing the steps in the belt removal procedure described above.

Another important feature of the subject invention is the transportability of the sanding machine which permits the device to be moved easily from lane to lane or from location to location. As shown in FIG. 8, this is accomplished by providing transporting wheels 236, 236' and 238, 238' on the bottom of rear subsection frame 14. These transporting wheels permit the sanding device to be tilted to a vertical position as shown in FIG. 11 and thus easily moved to a desired location.

FIG. 12 is a schematic diagram of an electrical circuit which may be used to control and operate the sanding machine of the present invention. A conventional power source 240 is connected by way of lines 242 and 244 to various control circuits which apply power to the belt drive motor 39, the tracking motor 126, the wheel drive motor 158 and leveling motor 214. The belt drive motor circuit includes an on-off switch 246 to control the current flow to the belt drive motor 39. In this preferred embodiment, the belt drive motor is a single direction-single speed motor of appropriate horsepower to rotate rear roller 34 to impart motion to belt 40; however, if desired, a reversible, variable speed motor may be used, and any suitable control switch may be provided for use with such a motor.

The wheel drive motor circuit has a three-position switch 250 such as a toggle switch, having forward, off and reverse positions to control the current to drive motor 158. Preferably the drive motor 158 will have a variable speed control (not shown) of any suitable type so that the speed at which the sander moves over the surface being sanded can be varied.

The leveling motor circuit has a remote push-button switch 218 which actuates reversible leveling motor 214. The push-button switch 218 is connected to the leveling motor 214 through the limit switch box 206. The limit switch 206 which is carried on cam shaft 198 operates to de-energize the leveling motor 214 to maintain shaft rotation within predetermined limits.

Any other suitable circuit means known in the art may be used to control the belt drive motor 39, wheel drive motor 158 and leveling motor 214.

Turning now to the operation of the belt tracking circuit, as described above and shown in FIG. 5, tracking lever 108 is provided to operate microswitches 116, 118, 120, 122, 124 and 126. The microswitches are two-position switches and power is applied to the first position of the microswitches at all times. Each of the switches is connected to a latching relay which operates to close an associated siwtch. For example, when switch 116 is not in contact with the projection 112 of lever arm 108, a latching relay coil 257 is energized, whereby switch 258 is in the closed position. When the microswitch 116 is operated by projection 112 and is moved to its second position, current passes through switch 258, since it was previously closed by relay coil 257. Current is then applied to a switch relay coil 260 which, in turn, closes switches 262 and 264 which are normally open. Upon closure of switch 264, power is applied to one side of the reversible motor 126 in order to operate the tracking mechanism, and upon closure of switch 262, power is applied to a timer 266A which operates after a specified time and closes normally open switch 266B momentarily. When switch 266B closes, power is applied to an unlatching relay coil 268 associated with switch 258 so that it will be opened, thus de-energizing relay coil 260 so that switches 262 and 264 will open and the tracking motor 126 and timer 266A are de-energized. position If the first operation of the tracking motor does of the move the tracking belt to a proper position which would cause the lever arm 108 to disengage from switch 116, it becomes necessary to operate the tracking motor 126 additional times in the same direction while switch'116 is disabled by remaining in contact with lever projection 112. Therefore, switches 118 and 120 have been provided to further correct the position for the abrasive belt.

Initially, switch 118 is in the first position; therefore, power is being applied to a latching relay coil 270 which closes switch 272. When switch 1 18 is contacted by the first step of the step projection 112 and moves to the second position, microswitch 116 is in contact with the second step of the projection. With switch 118 in the second position, current passes through switch 272 and energizes switch relay coil 260. Switches 262 and 264, which are normally open, are again closed, thus activating the tracking motor 126 and operating timer 266A. When timer 266A runs down, switch 266B ismomentarily closed, thereby applying power to unlatching relay coil 274 which opens switch 272. Relay coil 260 is then de-energized so that switches 262 and 264 are opened, thus taking power from the tracking motor 126 and operating timer 266A. In a similar manner, if the second correction is not enough, switch 120 will be contacted by the first stage of the step projection 112 andswitches 118 and 116 will be maintained in a closed position by the second and third steps, respectively, of the projection 112. The latching relay coil 276, switch 278 and unlatching relay coil 280 operate in a similar manner to corresponding components associated with microswitches 116 and 118, thus providing for a third position correction.

When the abrasive belt 40 moves to a proper position so that the lever 108 returns to a neutral position and none of the microswitches 116, 118,120 are in contact with the projection 112, the switches revert to their original position, whereby power is applied to the latching relay coils 257, 270, 276, respectively, thus closing switches 258, 272 and 278 so that they will be in position to operate again if the alignment of the endless belt becomes improper.

The other side of the belt tracking circuit operates similarly to the ones as described above; for example, the microswitches 122, 124 and 126 are in the first position and normally power is applied to latching relay coils 282, 284 and 286, respectively, thereby maintaining switches 288, 290 and 292 in the closed position.

When the belt 40 moves to the left, thus causing lever 108 to move to the left, as viewed in FIG. 5, step projection 114 contacts microswitches 122, 124 and 126 in that order. Upon contacting switch 122, and moving it to the second position, power passes through switch 288 and is applied to latching relay coil 294. Latching relay coil 294 closes normally open timer switch 296 and motor switch 298. Power is applied through switch 298 to the reverse side of tracking motor 126 and through switch 296 to timer 266A. Tracking motor 126 operates the belt tracking mechanism in a reverse direction in an effort to move the belt back to its proper position. When the timer 266A runs down, switch 2668 is closed momentarily, thereby applying power to unlatching relay coil 300, thus opening switch 288, so that the tracking motor 126 and timer 266A are deenergized. The remaining microswitches 124 and 126 on the left side of the tracking lever 108 are operated in the same manner that microswitches 188 and are operated, when the operation of the tracking motor caused by switch 122 is not of sufficient time to correct the position of the endless belt 40. Since the microswitch 122 will be in the second position and the un latching relay coil 300 will have opened the switch 288, it will be necessary to operate switches 124 and 126. Similarly, as has been explained above, the unlatching relay coil 302 associated with switch 124 and unlatching relay coil 304 associated with switch 126 are used to open switches 290 and 292, respectively, thus deenergizing the tracking motor.

It can be seen from the above description and drawings that the sanding machine described hereinabove provides means for easily transporting the machine from one location to another provides a leveling mechanism to maintain the machine in a level position to produce a horizontally sanded surface and also provides an automatic belt tracking control to maintain the abrasive belt in a preselected position on the carrying rollers.

As will be apparent to those skilled in the art, there are many variations and changes which can be made to the sanding machine; for example, the types of gearing arrangements may be changed, construction materials can be varied, or various types of level sensing means known in the art can be used. However, these and other variations and changes can be made in the invention as above described and illustrated without departing from the true spirit and scope thereof as defined in the following claims.

1 claim:

1. A sanding apparatus for sanding and refinishing horizontal surfaces, comprising:

a. frame means for said apparatus;

b. means for moveably mounting an abrasive belt means on said frame so that at least a portion of said belt will contact said horizontal surface;

c. at least one axle means for said frame;

(1. means for securing supportwheels to said axle means;

e. a first axle support member secured to said frame and adapted to receive one end of said axle means;

f. a leveling yoke pivotally secured at a first end to said frame and including at a second end a cam follower means;

g. a second axle support member adapted to receive the other end of said axle means, said second axle support member being mounted on said leveling yoke between said first and second ends of said yoke;

h. first cam means supported in said frame and contacting said cam follower means, said cam means being rotatable to move said follower, thereby to pivot said leveling yoke and adjust the position of said second axle support member with respect to said frame, whereby said other end of said axle means and the supporting wheel secured thereon is adjusted with respect to said frame to raise or lower one side of the frame and to maintain said portion of said belt in a horizontal position;

i. first drive means for selectively rotating said first cam means;

j. drive motor means connected to at least one of said support wheels for moving said sanding apparatus along said horizontal surface; and

k. belt tracking means for maintaining said abrasive belt in a preselected tracking position.

2. The sanding apparatus of claim 1 wherein said drive motor means is a variable speed reversible motor which enables said sanding apparatus to operate in first and second directions at a preselected speed, and further including switch means for selectively energizing said drive motor means.

3. The sanding apparatus of claim 1, wherein said cam means is eccentric.

4. The sanding apparatus of claim 1, wherein said cam means includes a first shaft journaled in said frame and carrying said cam means and wherein said drive means includes second motor means mounted on said frame and connected to said first shaft thereby to rotate said cam means to selected positions;

a. limit switch means for limiting the movement of said cam means; and

b. remote switch means for energizing said second motor means.

5. The sanding apparatus of claim 1, wherein said means for mounting said abrasive belt means includes:

a. a rear drive roller journaled on said frame with its axis of rotation approximately transverse to the direction of movement of said apparatus;

b. first and second pivot arms pivotally secured to a first and second side of the forward end of said frame; 1

c. a forward roller journaled in said first and second pivot arms, said forward roller having its axis of ro tation approximately parallel to the axis of rotation of said rear roller, said abrasive belt encircling the forward and the rear rollers;

(1. third motor means mounted on said frame for rotation said rear drive roller; and

e. means for energizing said third motor means.

6. The sanding apparatus of claim 1, wherein said belt tracking means includes:

a. means for sensing the position of said abrasive belt;

and

b. means responsive to said sensing means for returning said abrasive belt to said preselected position.

7. The sanding apparatus of claim 6, wherein said means for returning said abrasive belt to said preselected position includes means for adjusting the length of the path traveled by a first side of said abrasive belt. 6

a. first and second spaced roller means secured to said frame for receiving said belt,

b. mounting means including at least one pivot arm for adjustably mounting said first roller means on said frame;

c. second cam means supported in said frame;

d. second drive means for selectively adjusting said second cam means;

e. second cam follower means secured to said pivot arm, said second cam foller means engaging said second cam means to vary the position of said pivot arm in accordance with the adjustment of said second cam means, whereby the length of the path travelled by said belt is adjusted.

9. The sanding apparatus of claim 5, wherein said belt tracking means includes:

a. means for sensing the position of said abrasive belt;

and

b. means responsive to said sensing means for returning said abrasive belt to said preselected position.

10. The sanding apparatus of claim 9, wherein said means for returning said abrasive belt to said preselected position includes means for adjusting the length of the path traveled by a first side of said abrasive belt.

11. The apparatus of claim 10, wherein said means for adjusting the path traveled by a first side of said abrasive belt includes:

a. fourth motor means carried on said frame responsive to the means for sensing the position of said abrasive belt;

b. means for securing said first pivot arm of said forward roller means in a horizontal position;

c. cam means journaled in said frame and driven by said fourth motor means;

d. first lever means pivotally mounted to rotate about the pivotal axis of said second pivot arm, said lever means engaging said cam means and said second pivot arm, said lever means operating on said second pivot arm to vary the position of the second arm; and

e. first biasing means urging said lever means against said cam means, the movement of said second pivot arm causing the path traveled by said first side of said abrasive belt to be adjusted.

12. The sanding apparatus of claim 4, wherein said means for mounting said abrasive belt means includes:

a. a rear drive roller journaled on said frame with its axis of rotation approximately transverse to the direction of movement of said sanding apparatus;

b. first and second pivot arms pivotally secured to a first and second side of the forward end of said frame;

c. a forward roller journaled in said first and second pivot arms, said forward roller having its axis of rotation approximately parallel to the axis of rotation of said rear roller, said abrasive belt being mounted on side rear and forward rollers;

d. third drive means mounted on said frame for rotating siad rear drive roller; and

e. means for energizing said third drive means.

13. The sanding apparatus of claim 12, wherein said belt tracking means includes:

a. means for sensing the position of said abrasive belt;

and

b. means responsive to said sensing means for returning said abrasive belt to said preselected position.

14. The sanding apparatus of claim 13, wherein said means for returning said abrasive belt to said preselected position includes means for adjusting the length of the path traveled by a first side of said abrasive belt.

15. The sanding apparatus of claim 14, wherein said means for adjusting the path traveled by said first side of said abrasive belt includes:

a. fourth motor means carried on said frame responsive to said means for sensing the position of said abrasive belt;

b. means for securing said first pivot arm of said forward roller means in a horizontal position;

c. cam means journaled in said frame and driven by said fourth motor means;

d. first lever means pivotally mounted to rotate about the pivotal axis of said second pivot arm, said lever means engaging said cam means and said second pivot arm, said lever means operating on said second pivot arm to vary the position of said second arm; and

e. first biasing means urging said lever means against said cam means, the movement of said second pivot arm causing the path traveled by said first side of said abrasive belt to be adjusted.

16. The sanding apparatus of claim 8,wherein said means for sensing the position of said abrasive belt ineludes:

a. first switch means contacting said abrasive belt to sense movement of said abrasive belt; and

b. circuit means responsive to said first switch means for controlling said second drive means, said circuit means including means for energizing said second drive means when said abrasive belt moves from said preselected position and timing means for deenergizing said second drive means after a predetermined period of operation.

17. The sanding apparatus of claim 16, wherein said first switch means has plural positions whereby further movement of said abrasive belt re-energizes said second motor means for said predetermined period of time.

18. The sanding apparatus of claim 1, wherein said sanding apparatus is used for sanding bowling lanes and further includes guide wheel means carried on said frame which contact the rails between the bowling lanes to maintain the direction of movement of the sanding machine.

19. The sanding apparatus of claim 1, further including transporting wheels carried on the rear of said frame so that said machine can be pivoted to a vertical position for transporting to other locations.

20. The sanding apparatus of claim 1, further including position and repair wheel means for raising said frame from OH said horizontal surface.

21. The apparatus of claim 20, wherein said positioning and repair wheel means includes:

a. rear swivel wheels secured at the rear of said frame to the bottom surface;

b. forward wheels pivotally mounted to said frame;

and

c. means for pivoting said forward wheels into contact with said horizontal surface to raise the forward end of said frame and permit said rear swivel wheels to contact said horizontal surface.

22. The sanding apparatus of claim ll, wherein said belt tracking means includes means responsive to the position of said belt for adjusting said means for moveably mounting said belt to vary the length of the path travelled by one side of said belt with respect to the other side thereof.

23. The sanding apparatus of claim 22, wherein said axle means comprises first and second parallel spaced axles, each axle carrying a pair of spaced support wheels, and wherein said first axle is journaled in said frame.

24. The sanding apparatus of claim 23, wherein said first axle support member includes first and second ends for receiving said first and second axles, respectively, and is secured to said frame at a point intermediate said first and second ends.

25. The sanding apparatus of claim 23, wherein said second axle support member includes first and second ends for receiving said first and second axles, respectively, said second axle member being pivotally secured at its first end to said first axle and mounted on said leveling yoke at a point intermediate said first and second ends.

26. The sanding apparatus of claim 8, further including a platen secured to said frame, said platen extending across said apparatus and adapted to guide said abrasive belt against said horizontal surface. 

1. A sanding apparatus for sanding and refinishing horizontal surfaces, comprising: a. frame means for said apparatus; b. means for moveably mounting an abrasive belt means on said frame so that at least a portion of said belt will contact said horizontal surface; c. at least one axle means for said frame; d. means for securing support wheels to said axle means; e. a first axle support member secured to said frame and adapted to receive one end of said axle means; f. a leveling yoke pivotally secured at a first end to said frame and including at a second end a cam follower means; g. a second axle support member adapted to receive the other end of said axle means, said second axle support member being mounted on said leveling yoke between said first and second ends of said yoke; h. first cam means supported in said frame and contacting said cam follower means, said cam means being rotatable to move said follower, thereby to pivot said leveling yoke and adjust the position of said second axle support member with respect to said frame, whereby said other end of said axle means and the supporting wheel secured thereon is adjusted with respect to said frame to raise or lower one side of the frame and to maintain said portion of said belt in a horizontal position; i. first drive means for selectively rotating said first cam means; j. drive motor means connected to at least one of said support wheels for moving said sanding apparatus along said horizontal surface; and k. belt tracking means for maintaining said abrasive belt in a preselected tracking position.
 2. The sanding apparatus of claim 1 wherein said drive motor means is a variable speed reversible motor which enables said sanding apparatus to operate in first and second directions at a preselected speed, and further including switch means for selectively energizing said drive motor means.
 3. The sanding apparatus of claim 1, wherein said cam means is eccentric.
 4. The sanding apparatus of claim 1, wherein said cam means includes a first shAft journaled in said frame and carrying said cam means and wherein said drive means includes second motor means mounted on said frame and connected to said first shaft thereby to rotate said cam means to selected positions; a. limit switch means for limiting the movement of said cam means; and b. remote switch means for energizing said second motor means.
 5. The sanding apparatus of claim 1, wherein said means for mounting said abrasive belt means includes: a. a rear drive roller journaled on said frame with its axis of rotation approximately transverse to the direction of movement of said apparatus; b. first and second pivot arms pivotally secured to a first and second side of the forward end of said frame; c. a forward roller journaled in said first and second pivot arms, said forward roller having its axis of rotation approximately parallel to the axis of rotation of said rear roller, said abrasive belt encircling the forward and the rear rollers; d. third motor means mounted on said frame for rotation said rear drive roller; and e. means for energizing said third motor means.
 6. The sanding apparatus of claim 1, wherein said belt tracking means includes: a. means for sensing the position of said abrasive belt; and b. means responsive to said sensing means for returning said abrasive belt to said preselected position.
 7. The sanding apparatus of claim 6, wherein said means for returning said abrasive belt to said preselected position includes means for adjusting the length of the path traveled by a first side of said abrasive belt.
 8. The sanding apparatus of claim 7, wherein said means for adjusting the length of the path travelled by a first side of said abrasive belt includes: a. first and second spaced roller means secured to said frame for receiving said belt, b. mounting means including at least one pivot arm for adjustably mounting said first roller means on said frame; c. second cam means supported in said frame; d. second drive means for selectively adjusting said second cam means; e. second cam follower means secured to said pivot arm, said second cam foller means engaging said second cam means to vary the position of said pivot arm in accordance with the adjustment of said second cam means, whereby the length of the path travelled by said belt is adjusted.
 9. The sanding apparatus of claim 5, wherein said belt tracking means includes: a. means for sensing the position of said abrasive belt; and b. means responsive to said sensing means for returning said abrasive belt to said preselected position.
 10. The sanding apparatus of claim 9, wherein said means for returning said abrasive belt to said preselected position includes means for adjusting the length of the path traveled by a first side of said abrasive belt.
 11. The apparatus of claim 10, wherein said means for adjusting the path traveled by a first side of said abrasive belt includes: a. fourth motor means carried on said frame responsive to the means for sensing the position of said abrasive belt; b. means for securing said first pivot arm of said forward roller means in a horizontal position; c. cam means journaled in said frame and driven by said fourth motor means; d. first lever means pivotally mounted to rotate about the pivotal axis of said second pivot arm, said lever means engaging said cam means and said second pivot arm, said lever means operating on said second pivot arm to vary the position of the second arm; and e. first biasing means urging said lever means against said cam means, the movement of said second pivot arm causing the path traveled by said first side of said abrasive belt to be adjusted.
 12. The sanding apparatus of claim 4, wherein said means for mounting said abrasive belt means includes: a. a rear drive roller journaled on said frame with its axis of rotation approximately transverse to the direction of movement of said sanding apparatuS; b. first and second pivot arms pivotally secured to a first and second side of the forward end of said frame; c. a forward roller journaled in said first and second pivot arms, said forward roller having its axis of rotation approximately parallel to the axis of rotation of said rear roller, said abrasive belt being mounted on side rear and forward rollers; d. third drive means mounted on said frame for rotating siad rear drive roller; and e. means for energizing said third drive means.
 13. The sanding apparatus of claim 12, wherein said belt tracking means includes: a. means for sensing the position of said abrasive belt; and b. means responsive to said sensing means for returning said abrasive belt to said preselected position.
 14. The sanding apparatus of claim 13, wherein said means for returning said abrasive belt to said preselected position includes means for adjusting the length of the path traveled by a first side of said abrasive belt.
 15. The sanding apparatus of claim 14, wherein said means for adjusting the path traveled by said first side of said abrasive belt includes: a. fourth motor means carried on said frame responsive to said means for sensing the position of said abrasive belt; b. means for securing said first pivot arm of said forward roller means in a horizontal position; c. cam means journaled in said frame and driven by said fourth motor means; d. first lever means pivotally mounted to rotate about the pivotal axis of said second pivot arm, said lever means engaging said cam means and said second pivot arm, said lever means operating on said second pivot arm to vary the position of said second arm; and e. first biasing means urging said lever means against said cam means, the movement of said second pivot arm causing the path traveled by said first side of said abrasive belt to be adjusted.
 16. The sanding apparatus of claim 8, wherein said means for sensing the position of said abrasive belt includes: a. first switch means contacting said abrasive belt to sense movement of said abrasive belt; and b. circuit means responsive to said first switch means for controlling said second drive means, said circuit means including means for energizing said second drive means when said abrasive belt moves from said preselected position and timing means for de-energizing said second drive means after a predetermined period of operation.
 17. The sanding apparatus of claim 16, wherein said first switch means has plural positions whereby further movement of said abrasive belt re-energizes said second motor means for said predetermined period of time.
 18. The sanding apparatus of claim 1, wherein said sanding apparatus is used for sanding bowling lanes and further includes guide wheel means carried on said frame which contact the rails between the bowling lanes to maintain the direction of movement of the sanding machine.
 19. The sanding apparatus of claim 1, further including transporting wheels carried on the rear of said frame so that said machine can be pivoted to a vertical position for transporting to other locations.
 20. The sanding apparatus of claim 1, further including position and repair wheel means for raising said frame from off said horizontal surface.
 21. The apparatus of claim 20, wherein said positioning and repair wheel means includes: a. rear swivel wheels secured at the rear of said frame to the bottom surface; b. forward wheels pivotally mounted to said frame; and c. means for pivoting said forward wheels into contact with said horizontal surface to raise the forward end of said frame and permit said rear swivel wheels to contact said horizontal surface.
 22. The sanding apparatus of claim 1, wherein said belt tracking means includes means responsive to the position of said belt for adjusting said means for moveably mounting said belt to vary the length of the path travelled by one side of said belt with respect to the other side thereof.
 23. The sanding apparatus of claim 22, wherein said axle means comprises first and second parallel spaced axles, each axle carrying a pair of spaced support wheels, and wherein said first axle is journaled in said frame.
 24. The sanding apparatus of claim 23, wherein said first axle support member includes first and second ends for receiving said first and second axles, respectively, and is secured to said frame at a point intermediate said first and second ends.
 25. The sanding apparatus of claim 23, wherein said second axle support member includes first and second ends for receiving said first and second axles, respectively, said second axle member being pivotally secured at its first end to said first axle and mounted on said leveling yoke at a point intermediate said first and second ends.
 26. The sanding apparatus of claim 8, further including a platen secured to said frame, said platen extending across said apparatus and adapted to guide said abrasive belt against said horizontal surface. 